Pressure exchangers



" 1963 J. A. c. KENTFIELD PRESSURE EXCHANGERS 2 SheetsSheet 1 Filed Dec. 22. 1961 1963 J. A. c. KENTFIVELD 3,109,580

PRESSURE EXCHANGERS Filed Dec. 22, 1961 2 he tsh t 2 He. 5. H6. 6.

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United States Patent 3,109,580 PRESSURE EXCHANGERS John Alan Charles Kentfield, Worthing, Sussex, England, assignor to Power Jets (Research & Development) Limited, London, England, a British company Filed Dec. 22, 1961, Ser. No. 161,705 Claims priority, application Great Britain Jan. 20, 1961 4 Claims. (Cl. 230-69) This invention relates to pressure exchangers.

The term pressure exchanger is used herein to mean apparatus comprising cells in which one fluid quantity expands so compressing another fluid quantity with which it is in direct contact, ducting to lead fluid at difierent pressures substantially steadily to and from the cells, and means to effect relative motion between the cells and the ducting.

customarily, the cells are mounted as a cell ring, which may be arranged for rotation, and the ducting communicates with the cells through ports in end-plates disposed immediately adjacent the open ends of the cells.

One of the disadvantages of a pressure exchanger is the noise generated during operation. The use of silencers for gas streams leaving and entering the apparatus and soundinsulating lagging around the apparatus as a whole has a merely palliative effect and such use does nothing towards the reduction of the noise at its source.

The object of the present invention is to reduce the noise generated by a pressure exchanger during operation.

The invention will now be explained with the aid of the accompanying diagrammatic drawing, in which:

FIGURE 1 is an exploded perspective view of a conventional pressure exchanger;

FIGURE 2 is a fragmentary end elevation of one embodiment of a pressure exchanger cell ring in accordance with the invention;

FIGURE 3 is a fragmentary end elevation of another embodiment of a pressure exchanger cell ring in accordance with the invention;

FIGURE 4 is a fragmentary end elevation of a third embodiment of a pressure exchanger cell ring in accordance with the invention; and

FIGURES 5 and 6 are details of cell ring construction of the pressure exchanger illustrated in FIGURE 4.

Referring now to FIGURE 1 of the drawings the pressure exchanger includes a cell ring having a multiplicity of radial walls 1 arranged around a hub 2 and having a cylindrical shroud 3. Cells defined by the walls 1, the hub 2 and the shroud 3 are in themselves open-ended but the effective opening of the cells is controlled by endplates 4 having ports 5, 6, 7 and 8 to lead fluid to and from the cells. In the example shown high-pressure fluid is admitted through the port 5, low-pressure fluid is admitted through the port 6, high-pressure fluid leaves through the port 7 and low-pressure fluid leaves through the port 8. Ducts corresponding to these ports are referenced 9, 10, 11 and 12. It Will be appreciated that the ports and ducts illustrated have been made of smaller circumferential extent than would be used in practice. A shaft (not shown) passes through bores 13, 14, 15 in the cell ring and end-plates.

It has been found by experiment that the frequency of the primary mode of oscillation of the noise emitted by a pressure exchanger during operation, corresponds directly to the frequency with which the cells move past a fixed point. One way in which this primary mode of oscillation may be raised above the upper limit of audiofrequency is by increasing the number of cells in the cell ring. However, such an increase will need to be considerable in relation to the number of cells hitherto suggested. Furthermore, such an increase leads to difficulties, the most important being a substantial increase in the buildice up of boundary layer fluid in the cells, which will bring about a. loss in efllciency of the pressure exchanger. If the mean width of a cell falls below a certain minimum, then the amount of boundary layer fluid along each cell wall will be inconveniently large. When the mean width of the cell is very small in comparison with the length of the cell, the boundary layer fluid along each cell wall will meet and will then occupy the whole of the cross-sectional area of the cell. To ensure that the boundary layer fluid does not give rise to a loss in efliciency, the ratio, 6,

time taken -for cell to become fully open at a port time taken for wave to traverse the length of the cell may not be less than about 0.3, the exact value being established by experiment.

The following derived expression gives a relationship between I the axial length of each cell in feet; the number of cells n in the cell ring; the ratio 6; the local velocity of sound a in feet/second; rotational speed of the cell ring N in rpm; and the frequency f with which a cell passes any fixed point.

The time for a cell to become fully open at a port seconds N n The time for a wave to traverse the length of the cell l seconds i Nn l (1) The frequency with which a cell passes a fixed point f 1= per second Hence, from Equations 1 and 2 The limit of audio-frequency ;l6,000 c.p.s.

Since the frequency with which a cell passes a fixed point corresponds directly to the frequency of the primary mode of oscillation of the pressure exchanger during operation, then in order that this primary mode of oscillation is above the limit of audio-frequency fcellz 6, 0.13.3.

16,000 a has A cell ring construction which enables a large number of cells to be accommodated, but conforming with the expression derived above, is shown in FIGURE 2. The length of each cell will be less than has been proposed hitherto, but more than is called for with a cell ring having only one ring of cells conforming to the expression lated to the product of the rotational speed and the total number of cells in all three rings.

The embodiment of FIGURE 3 is an inversion of the embodiment of FIGURE 2. The corresponding cell walls of each ring lie in the same radial plane, and the required noise frequency is achieved by the provision of ports such as 28 (shown in chain lines), the opening and closing edges of which are divided into three portions corresponding to the rings of cells, each portion lying on a different radius. It will be seen that although inverted, the embodiment of FIGURE 3 operates effectively in the same manner as that of FIGURE 2. Compared with a pressure exchanger including a cell ring conforming to the derived expression and having only a single ring of cells, the cell rings illustrated in FIGURES 2 and 3 permit, for the same number of cells, the cells to be of greater mean width and therefore of greater axial length.

In certain circumstances the embodiments of FIGURES 2 and 3 would not be convenient. A fragment of a cell ring with a single ring of cells is illustrated in FIGURE 4. Again, the dimensions of the cell ring conform to the expression N n at; 16,0005 6 in which 6 is, of course, not less than 0.3. It is expected that from 160 to 180 cells will be required if the length of the cells is not to be too small or the speed of revolution too high. Each wall 30 is arcuate but has hooked edges 31 as shown in detail in FIGURE or swaged edges 32 as shown in FIGURE 6. The walls may be curved to form an arc of a circle or may be in the form of a catenary and will inevitably be of thinner cross-section than in pressure exchangers proposed previously. For either form of well the stresses can be readily pre-determined and the fixing moment at the edges is zero.

I claim:

1. A pressure exchanger including a hub means, a plurality of open-ended cells arranged around the hub means, the hub means and the plurality of open-ended cells constituting a cell ring, end-plate structure at each end of the cell ring, ports in the end-plate structure for the admission of fluid to and the extraction of fluid from the cells, the cell ring having a relationship of N n a Z 16,000fi where N is the rotational speed of the cell ring in r.p.m., n is the number of cells; a is the local velocity of sound in feet/ second; I is the axial length of each cell in 'feet and time taken for cell to become fully open at a port time taken for a wave to traverse the length of the cell {2. A pressure exchanger as claimed in claim 1, in which the cells are arranged as two or more concentric rings, the individual cell walls of each cell ring being staggered in relation to the individual cell walls of the other cell ring or rings.

3. A pressure exchanger as claimed in claim 1, in which the cells are arranged as two or more concentric rings,

the individual cell Walls of each cell ring being in line References Cited in the file of this patent UNITED STATES PATENTS 2,675,173 Iendrassik Apr. 13, 1954 2,764,340 .Tendrassik Sept. 25, 1956 FOREIGN PATENTS 840,408 Great Britain July 6, 1960 

1. A PRESSURE EXCHANGER INCLUDING A HUB MEANS, A PLURALITY OF OPEN-ENDED CELLS ARRANGED AROUND THE HUB MEANS, THE HUB MEANS AND THE PLURALITY OF OPEN-ENDED CELLS CONSTITUTING A CELL RING, END-PLATE STRUCTURE AT EACH END OF THE CELL RING, PORTS IN THE END-PLATE STRUCTURE FOR THE ADMISSION OF FLUID TO AND THE EXTRACTION OF FLUID FROM THE CELLS, THE CELL RING HAVING A RELATIONSHIP OF 